A well-known method of precision synchronization pulse separation is described in AMPEX, TBC-3, CAT. NO. 1809636-01, February 1985, 401 Broadway, where the composite videosignal is filtered by the color carrier, after which it is compared with the trimming level--50% sync, produced by level black detection and level sync detection as a mean value of both.
A disadvantage of the known method is its complex technical implementation since it requires a number of supplementary processings steps such as rough sync pulse separation, key detection by memorizing the levels determining the sync signal amplitude, and termination of the key detections of levels during the attenuation intervals by frames, in drop-outs and pulse noises. The latter demands level averaging for larger time intervals, which reduces the separation precision. This precision is reduced to a certain extent also by the need for preliminary frequency signal filtration related to the shifting of the front, or the separated sync pulses, respectively.
There is a well known device for the implementation of the well-known method I1I consisting of a filter for the color carrier connected by its output to one of the inputs of a level comparator and simultaneously to the input of a rough sync selector--about 25% with respect of level black, the output of which is connected to two key pulse shapers--for sync peak and for rear platform connected to the key inputs of two dynamic sample/hold memories. The signal inputs of the latter are connected to the output of the color carrier filter and their outputs are connected to the inputs of an adder. The latter's output is coupled to the second input of the level comparator the output of which is an output of the sync separator. The disable input of the rough sync separator is connected to the output of frame blanking pulse shapers and apply the drop-out disable pulse across an OR gate.
A disadvantage of this device is its high degree of complexity and reduced precision as a result of a need for dynamic memory with large-value time constants. The system also gives rise to a deformation of the sync fronts as a result of high frequency filtration.
Another somewhat simplified device implementing the well-known I2I method is also known and is designed for incorporation in integrated sync processors. This device has a limiter--sync separator, by a detector at level black connected to a second detector at level sync, the output of which is connected to one of the inputs of a differential amplifier, across the second input of which is connected the composite sync signal, its output being an output of the device.
A disadvantage of this device is its low precision due to the need to use large time-constants for the level detectors. This makes its application for professional needs inadequate.